1. Field of the Invention
The invention relates in general to methods and devices for mechanically testing the tensile strength of an article, and, more particularly, embodiments of the present invention relate to jack bolt activated tensile strength testing machines.
2. Description of the Prior Art
Tensile strength testing machines and methods have been widely used for many years for determining the mechanical tensile strengths of various articles. The prior art devices and methods are not without their shortcomings. A major shortcoming of typical prior art devices and methods is that they are expensive to purchase and rely, for example, on hydraulic activators, or the like, which require maintenance, repair, and some skill in their operation. They are generally not quick enough or simple enough to use for purposes of proof testing manufactured articles in a manufacturing operation for purposes of quality control.
Some articles of manufacture are of such a critical nature that every one or at least a large percentage of those made must be tested individually to determine whether they meet predetermined strength requirements. This is generally referred to as proof testing. Such testing must be done on a continuous basis as a part of a manufacturing operation. It must be done quickly and easily, and the testing equipment must be reliable, rugged, and simple to operate. The costs of purchasing, maintaining and operating such proof testing equipment must be low. Previously proposed expedients tended to be unsuitable for use in a manufacturing environment, among other reasons, because of costs, complexity, maintenance cost, or slow cycle times.
Many devices had been proposed for the purposes of measuring and indicating mechanical strain. The indicating elements typically included, for example, visible read outs or printouts, data loggers, or the like. The measuring devices typically included compression and tension load cells and strain gauges of various types.
The use of jack bolts in a collar that surrounds and is in an axially fixed position relative to a bolt for purposes of imposing large loads on the shank of the bolt is known. See, for example, Alba U.S. Pat. No. 6,199,925, and Steinbock U.S. Pat. No. 5,083,889. Torquing down the jack bolts one by one permits the quick and simple imposition of very substantial loads on the shank of the bolt.
Swiveling hoist rings are widely used for safely lifting heavy loads in many different industries. Various swiveling hoist rings are shown, for example, in Tsui U.S. Pat. No. 5,405,210, and Alba U.S. Pat. No. 6,267,422. Because they are critical safety devices, swiveling hoist rings must be proof tested by their manufacturer. Proof testing generally involves placing the hoist rings in tension with a load that equals twice the rated capacity of the hoist ring. Thus, a hoist ring that is, for example, rated at a lifting capacity of 20,000 pounds is designed to have an ultimate strength of 100,000 pounds, and must (by government regulation) be proof tested to double its rated load, or 40,000 pounds. The test loads are imposed in tension. At least during the design phase of a new hoist ring, and following changes in an existing hoist ring product, it is tested to failure. If a test specimen of a hoist ring design fails at 80,000 pounds, it would not be rated at more then 16,000 pounds load capacity. The test equipment that is used for these tests must be certified as to accuracy. Reliable, certifiable, convenient, and inexpensive testing equipment is required to perform such tests.
These and other difficulties of the prior art have been overcome according to the present invention.